This invention relates to a method of producing an article having a structurally primary part obtained by press-forming of a metal sheet and a structurally secondary part which is stuck to the primary part with an adhesive. For example, the article may be a vehicle body part wherein the secondary part is provided for decorative or cushioning purpose.
Various articles, or some parts thereof, are produced through the steps of forming a structurally primary part by press-forming of a metal sheet and sticking a structurally secondary part which serves, for example, a decorative or cushioning purpose to the primary part by using an adhesive. In automobiles for instance, door trim panels are largely produced through such steps, using a sheet of a relatively soft and elastic material such as textile, nonwoven fabric or synthetic resin processed into artificial leather as the aforementioned secondary part.
Considering more in detail, press-forming of the primary part is accomplished through the following sub-steps: (a) blanking of metal sheet, (b) application of lubricating oil to the blank, (c) press-forming, (d) degreasing for removal of the lubricating oil from the press-formed metal part, (e) cleansing of the degreased metal part, (f) drying of the cleansed metal part, and (g) disposal of the chemicals used in the degreasing step and washings in the cleansing step. In a practical press-forming operation for sheet metal, it is an indispensable requisite to use a lubricant for accomplishment of smooth operation and production of a defectless metal part. Naturally the lubricant remains on the surfaces of the press-formed metal part.
It has commonly been recognized that adhesion-bonding of a secondary part to the press-formed metal part must be preceded by complete removal of the lubricant from the metal part because the presence of the lubricant between the metal part surface and an adhesive layer for sticking of the secondary part constitutes a serious obstacle to the establishment of strong adhesion between the secondary part and the primary metal part. It is impossible or impracticable to achieve complete removal of the lubricant merely by a physical cleaning method, and therefore the aforementioned degreasing step is performed by chemical treatment of the press-formed metal part. Then it becomes necessary to completely cleanse the chemicals used for degreasing from the degreased metal part because the presence of such chemicals is also detrimental to the subsequent adhesion operation. The cleansed metal part must be dried, and the waste lubricant and degreasing agent as well as the washings in the cleansing step must be disposed through suitable treatments. These sub-steps (d), (e), (f) and (g), though can be regarded as subsidiary steps, are considerably troublesome operations and constitute significant factors of the total production cost.